The Door into Summer

The novel follows engineer Daniel Boone Davis, who is betrayed by his business partner and fiancée, then placed into cold sleep. He awakens decades later in the year 2000 and, using time-travel technology, loops back to orchestrate revenge and reclaim his stolen company and beloved pet cat, Petronius the Arbiter.

A Japanese live-action film adaptation of The Door into Summer was released in 2021, updating Heinlein's 1957 cold-sleep and time-travel narrative for a contemporary audience. Prior to that, the novel had circulated in Hollywood development for years without a produced project.

The novel moves between the 1970s—when protagonist Dan Davis enters cold sleep—and the future year 2000, where he awakens. A second time-travel jump back to 1970 creates a loop that allows Davis to reshape events and resolve the plot's betrayals.

The Door into Summer was first published in 1957 by Doubleday, as one of Heinlein's novels aimed at an adult audience rather than his Scribner's juvenile line. It had earlier appeared in serial form in The Magazine of Fantasy and Science Fiction before being expanded into a full-length novel.